This invention relates to an airbag assembly for a motor vehicle and specifically to a variable inflation force inflator for an airbag assembly.
Typically, an airbag assembly includes an airbag cushion and an inflator. Conventional inflator assemblies include a detonator to trigger a gas-producing chemical. Triggering the gas-producing chemical produces a large quantity of rapidly expanding gas that inflates the airbag cushion. The inflator is typically triggered electrically by way of an electronic control module positioned within a motor vehicle. The rapidly expanding gas that inflates the airbag cushion exerts a large force in a relatively short duration of time. This large force is a product of the speed in which an airbag must fully inflate in order to provide impact prevention to occupants of the vehicle during a collision.
The force of inflation is set at a level such that an occupant of normal size and weight will not be injured. The required force to inflate an airbag cushion varies depending on the specific size and weight of the occupant. Injury to occupants is a design consideration taken into account when determining the magnitude of airbag inflation force.
Warnings, along with devices that simply turn the air bag off upon sensing specific conditions are currently in use to warn and protect against possible injury. In some instances a simply switch is installed to turn off the airbag. Other devices sense the size or weight of the occupant and activate the airbag only under a predefined set of conditions. It is well proven that airbag cushions provide an additional level of safety to an occupant during a collision. Devices that disable the airbag remove this level of safety to the possible detriment of smaller occupants.
For this reason, it is desirable to develop an airbag assembly that can inflate at various force levels such that the safety benefits of an airbag cushion can be used for occupants of all sizes.
An embodiment of this invention is an inflator for an airbag assembly including a plurality of independently actuatable gas generating units to vary inflation force of an airbag cushion.
An embodiment of this invention includes a plurality of gas generating units mounted to an igniter holder. Each gas-generating unit includes an outer periphery including a plurality of gas output openings. The igniter holder is generally a cylinder defining an outer surface and an inner cavity. Igniters are disposed within the inner cavity at discrete locations along an axis. Each of the igniters are electrically connected to a control unit by way of electrical leads. The igniters are mechanically isolated from each other to prevent actuation of one igniter in response to the actuation of an adjacent igniter.
In one embodiment, the igniters are isolated by a hardenable compound packed into the igniter holder. Alternatively, interior walls are disposed within the cavity and between the igniters to separate the igniters and prevent actuation of one igniter from setting off an adjoining igniter.
Each gas-generating unit is formed from a first and second stamped metal housing. The first and second stamped housings include overlapping tab sections at the contact point therebetween. The overlapping tab sections seal a compartment formed between the first and second metal housings. The tab sections are not mechanically attached to each other. Instead, the housings are forced into contact and remain in contact by way of pressure applied from a securing member attached to the end of the igniter holder.
The compartment formed between the first and second metal housings includes the pyrotechnic compound and a gas filter. The compartment includes an angle alpha between the first and second metal housings, such that the width decreases as the perpendicular distance from the axis increases so that gas generated by the pyrotechnic compound will be forced through the gas filter. To minimize heat from one gas-generating unit from igniting an adjacent gas-generating unit a thermal screen is disposed between each gas-generating unit.
The inflator of this invention preferably includes three gas-generating units of differing size and power. The power correlates to the amount of pyrotechnic material disposed in each compartment. A controller is used to selectively ignite each gas-generating unit based on various parameters sensed within the motor vehicle
The inflator assembly of this invention includes multiple gas-generating units or chambers including an individually actuated igniter that allows control over inflation of the airbag cushion to vary the magnitude of force exerted by the airbag cushion during inflation.